U.S. Pat. Nos. 7,140,569 and 7,621,477, which are both incorporated by reference in their entirety herein and are both to Young, note several industries rely on impact grinders or hammermills to reduce materials to a smaller size. For example, hammermills are often used to process forestry, agricultural products, and minerals and to recycle materials. Materials processed by hammermills include grains, animal food, pet food, food ingredients, mulch, and bark.
Whole grain corn must be cracked before further processing and may be cracked after tempering yet before conditioning. Particle size reduction may be accomplished with a hammermill including successive rows of rotating hammer like devices spinning on a common rotor next to one another comminute the grain product. Several methods for size reduction as applied to grain and animal products are described in Watson, S. A. & P. E. Ramstad, ed. (1987, Corn: Chemistry and Technology, Chapter 11, American Association of Cereal Chemist, Inc., St. Paul, Minn.), the disclosure of which is hereby incorporated by reference in its entirety.
Hammermills may also be generally referred to as crushers and typically include a steel housing or chamber containing a plurality of hammers mounted on a rotor and a suitable drive train for rotating the rotor. As the rotor turns, the correspondingly rotating hammers come into engagement with the material to be comminuted or reduced in size. Hammermills typically use screens formed into and circumscribing a portion of the interior surface of the housing. The size of the particulate material is controlled by the size of the screen apertures against which the rotating hammers force the material. Exemplary embodiments of hammermills are disclosed in U.S. Pat. Nos. 5,904,306; 5,842,653; 5,377,919; and 3,627,212, which are all incorporated herein.
Swinging hammers with blunt edges are typically better suited for processing “dirty” products, or products containing metal or stone contamination. The rotatable hammers of a hammermill may recoil backwardly if the hammer cannot break or push the material on impact. Even though a hammermill is designed to better handle the entry of a “dirty” products, there still exists a possibility for catastrophic failure of a hammer causing severe damage to the hammermill and requiring immediate maintenance and repairs.
Treatment methods such as adding weld material to the end of the hammer blade improve the comminution properties of the hammer. These methods typically infuse the hammer edge, through welding, with a metallic material resistant to abrasion or wear such as tungsten carbide. See for example U.S. Pat. No. 6,419,173, incorporated herein by reference, describing methods of attaining hardened hammer tips or edges as are well known in the prior art by those practiced in the arts.
Hammers are typically singular units and are not rigidly secured together. For example, as is shown in FIGS. 1-4 of U.S. Pat. No. 7,140,569, the hammers may be slid onto a drive shaft and spacers are placed in between each hammer. This configuration presents many potential gaps, all of which are exposed to debris, thereby creating excessive or premature wear. It is therefore desirable to minimize the number of parts and the corresponding number of gaps to extend the life of the hammer assembly.
The use of separate hammers and spacers also presents removal and installation difficulties. While some parts may be keyed to the drive shaft, flying debris can dent or damage parts thereby making removal or installation difficult. The increased number of parts also complicates the assembly/disassembly process. Thus, there is a need in the art to simplify the installation and replacement process and to minimize the number of parts being replaced.
The four metrics of strength, capacity, run time, and the amount of force delivered are typically considered by users of hammermill hammers to evaluate any hammer to be installed in a hammermill. A hammer to be installed is first evaluated on its strength. Typically, hammermill machines employing hammers of this type are operated twenty-four hours a day, seven days a week. This punishing environment requires strong and resilient material that will not prematurely or unexpectedly deteriorate. Next, the hammer is evaluated for capacity, or more specifically, how the weight of the hammer affects the capacity of the hammermill. The heavier the hammer, the fewer hammers that may be used in the hammermill by the available horsepower. A lighter hammer increases the number of hammers that may be mounted within the hammermill for the same available horsepower. More force delivered by the hammer to the material to be comminuted against the screen increases effective comminution (e.g. cracking or breaking down of the material) and efficiency of the comminution process. The force delivered is evaluated with respect to the weight of the hammer. Finally, the longer the hammer lasts, the longer the machine is able to run, resulting in larger profits presented by continuous processing of the material in the hammermill through reduced maintenance costs and lower necessary capital inputs. The four metrics are interrelated and typically tradeoffs are necessary to improve performance. For example, to increase the amount of force delivered, the weight of the hammer could be increased. However, because the weight of the hammer increased, the capacity of the unit typically will be decreased because of horsepower limitations. There is a need in the art to improve upon the design of hammermill hammers available in the prior art for optimization of the four (4) metrics listed above.